The proposal is a study of the basic biochemical control of serine biosynthesis in vivo. The project may be subdivided into three parts: 1) The purification and detailed kinetic analysis of the enzymes of the phosphorylated pathway of serine synthesis; D-3-phosphoglycerate dehydrogenase, phosphoserine aminotransferase and phosphoserine phosphatase; 2) The determination of the equilibrium constants under physioloical conditions for the reactions of the non-phosphorylated pathway of serine biosynthesis; D-glygerate dehydrogenase and hydroxypyruvate aminotransferase; and 3) The determination in tissue extracts of key intermediates in the pathway of serine synthesis; D-3-phosphoglycerate, phosphoserine, serine, 2-phosphoglycerate, phosphate, alanine, glutamate, 3-ketoglutarate, malate, lactate, pyruvate, and oxaloacetate.